Wireless local area networks (WLANs) may include an access point (AP) and one or more client stations. Various operating standards for WLANs include, but are not limited to, Institute for Electrical and Electronics Engineers (IEEE) 802.11a, 802.11ac, 802.11af, 802.11ah, 802.11b, 802.11g, and 802.11n.
An access point periodically transmits a beacon frame at a target beacon transmission time (TBTT) and/or, in some 802.11 operating standards, a short beacon frame at a target short beacon transmission time (TSBTT). Each of the beacon frame and the short beacon frame may include a timestamp used for a timing synchronization function (TSF). For example, each client station in a basic service set (BSS) of the WLAN may use the timestamp in a beacon frame to synchronize timing between the AP and the client station. FIG. 1A shows an example beacon frame 100. FIG. 1B shows an example short beacon frame 104. FIG. 1C shows an example timing diagram 108 of transmission of the beacon frames 100 at TBTTs 110 and the short beacon frames 104 at TSBTTs 112.
The beacon frame 100 includes a media access control (MAC) header portion 116, which includes, for example only, a frame control field 120, a duration field 124, address fields 128 (e.g., including a source address, a destination address, etc.), a sequence control field 132, and, in some standards (e.g., 802.11n), a high throughput (HT) control field 136. The beacon frame 100 also includes a frame body field 140 and a frame check sequence (FCS) field 144. The frame body field 140 includes, for example only, an 8 byte timestamp field 148, a beacon interval field 152, a capability field 156, a service set identifier (SSID) field 160, a supported rates field 164, and a frequency hopping (FH) parameter set field 168 and other information elements associated with BSS operation.
The short beacon frame 104 includes a frame control field 172, a duration field 176, a source address field 180, a 4 byte timestamp field 184, a change sequence field 188, a next TBTT field 192, a compressed SSID field 196, an access network options field 200, optional information elements (lEs) 204, and an FCS field 208. The optional IEs 204 include a short beacon compatibility element 212, which includes, for example only, an element ID field 216, a length field 220, a capability field 224, a beacon interval field 228, and a TSF completion field 232.